1. Field of the Invention
The present invention relates to a lens barrel having an optical element which is deformed by its own weight and/or by being held in position and also to a projection aligner having the lens barrel. More particularly, the present invention relates to a lens barrel having, as such an optical element, for example, a binary-type diffractive optical element and to a projection aligner having the lens barrel.
2. Description of Related Art
Optical systems of the kind having diffractive optical elements have been developed in various manners during recent years. The diffractive optical elements known to be used for the optical systems include, for example, Fresnel zone plates, kinoforms, binary optics and hologram elements.
The diffractive optical element is used for converting an incident wavefront into a predetermined wavefront and has features not possessed by a refraction-type lens. For example, the diffractive optical element has dispersion reverse to that of the refraction-type lens and can be formed thin, so that the whole optical system can be compactly constructed.
Generally, with the diffractive optical element arranged to be in a binary type shape, the diffractive optical element can be manufactured by using the manufacturing technique for semiconductor devices. With such a manufacturing technique applied, the diffractive optical element can be manufactured without difficulty to have fine pitches. In view of this, researches are being actively conducted for a binary-type diffractive optical element of the blazed shape which approximates to a stepped shape.
Meanwhile, various methods have been employed for positioning optical elements, such as a diffractive optical element, a lens, etc., within a lens barrel. The known methods include a lens pressing method, a throw-in method, etc.
FIG. 1 shows in outline the structural arrangement of a lens barrel in which optical elements are positioned by the lens pressing method. Referring to FIG. 1, lenses 8 are arranged to constitute a projection optical system. The lens barrel 9 is arranged to hold the lenses 8. Retaining rings 10 are arranged in the lens barrel 9 to fix the lenses 8 to their positions by causing the lenses 8 to abut on the respective lens setting parts xe2x80x9caxe2x80x9d of the lens barrel 9.
The outside shapes of the lenses 8 are beforehand cut to be coaxial with respect to a lens optical axis La by machining to a predetermined degree of precision, and the outside diameters of them are beforehand measured and determined also to a predetermined degree of precision.
The inside diameter of the lens barrel 9 is beforehand cut and determined according to the outside diameters of the lenses 8 measured, in such a way as to have a predetermined clearance between the inside diameter of the lens barrel 9 and the outside diameter of each of the lenses 8 when the lenses 8 are fitted in the lens barrel 9.
The lenses 8 are positioned in the direction of the optical axis La by screwing a male screw part formed on the peripheral part of each of the retaining rings 10 into the corresponding one of female screw parts 90 formed in the inner side wall of the lens barrel 9. Each of the retaining rings 10 is thus screwed to cause each of the lenses 8 to abut on the corresponding lens setting part xe2x80x9caxe2x80x9d, so that the lenses 8 are fixed in position.
In the case of the conventional lens barrel shown in FIG. 1, since each of the lenses 8 is pushed against the corresponding lens setting part xe2x80x9caxe2x80x9d, the surface shape of each of the lenses 8 tends to be deformed according to the shape of the retaining ring 10 and the shape of the lens setting part xe2x80x9caxe2x80x9d. Such deformation has presented such a problem as to cause the optical characteristics of the lenses 8 to vary,
To solve the above problem, it is possible to lessen a pushing force on the lens 8, by sticking the lens 8 to the inner wall of the lens barrel 9 by adhesives without using the retaining ring 10. However, in a case where the direction of the optical axis coincides with the direction of gravitation, the lens 8 might be sometimes deformed by its own weight to some extent and in some directions according to the shape of the lens setting part xe2x80x9caxe2x80x9d.
It is difficult to machine the lens setting part with its flatness kept more accurate than the flatness of the lens surface. It is also difficult to accurately presume the deformation of the lens abutting on the lens setting part beforehand, because the shape of the lens setting part in each of lens barrels differs from that in another lens barrel. Therefore, in the case of an optical system where even a minute amount of deformation is considered to be a serious drawback, the optical performance of the optical system must be evaluated after assembly work of the optical system and the posture or position of each lens must be adjusted according to the result of the evaluation in a prescribed manner to correct various aberrations resulting from the surface deformation. Accordingly, the number of necessary assembly and adjustment processes has been increased by such additional processes that are necessary.
Further, in a case where a thin optical element such as a diffractive optical element or the like is to be held by a lens barrel, in particular, the amount of the above-stated deformation becomes too much to obtain a desired optical performance by adjusting the posture or position of the optical element.
The invention is directed to the solution of the above-stated problems of the prior art. Therefore, it is an object of the invention to provide a lens barrel and a projection aligner, which improve upon the prior art.
To attain the above object, in accordance with an aspect of the invention, there is provided a lens barrel, which comprises an optical element having a light-transmissive surface which is deformed by its own weight and/or by being supported, and a plurality of protrusive parts which support the optical element, the plurality of protrusive parts being disposed in such a way as to enable the light-transmissive surface of the optical element to be deformed symmetrically with respect to a plane which includes an optical axis.
Further, in the lens barrel, when the optical element includes a pair of optical elements, the pair of optical elements are arranged to mutually correct variations of optical characteristics thereof caused by deformation thereof.
Further, the lens barrel further comprises a lens which corrects a variation of optical characteristics of the optical element caused by deformation of the optical element.
Further, in the lens barrel, each of the plurality of protrusive parts are arranged to be substantially in point-contact with the optical element.
Further, in the lens barrel, positions of the plurality of protrusive parts in a direction of the optical axis are the same.
Further, in the lens barrel, the number of the plurality of protrusive parts is two, three, four, five, six, seven, eight or nine.
Further, in the lens barrel a plurality of points of a peripheral part of the optical element are stuck to an inner wall of the lens barrel by an adhesive.
Further, in the lens barrel, the optical element is a lens or a mirror.
Further, in the lens barrel, the optical element is a diffractive optical element.
Further, the lens barrel further comprises a plurality of optical elements each having a light-transmissive surface which is substantially deformed by its own weight and/or by being pressed, the plurality of optical elements including lenses and/or mirrors.
Further, in the lens barrel, each of the plurality of protrusive parts is in a semispherical shape or pin-like shape.
Further, in the lens barrel, the plurality of protrusive parts are disposed in such a way as to enable the light-transmissive surface to be deformed symmetrically with respect to both a first plane which includes the optical axis and a second plane which includes the optical axis and is perpendicular to the first plane.
In accordance with an other aspect of the invention, there is provided a lens barrel, which comprises an optical element having a surface which is deformed by its own weight, and means for supporting the optical element so that the surface of the optical element is deformed symmetrically with respect to at least one plane which includes an optical axis substantially only by its own weight.
In accordance with a further aspect of the invention, there is provided a lens barrel, which comprises an optical element having a surface which is deformed by its own weight and by being supported, and means for supporting the optical element so that the surface of the optical element is deformed symmetrically with respect to at least one plane which includes an optical axis substantially only by its own weight and by being supported.
In accordance with a further aspect of the invention, there is provided a lens barrel, which comprises a plurality of optical elements, the plurality of optical elements including a lens and/or a mirror, at least one optical element having a light-transmissive surface which is deformed by its own weight and/or by being supported, and two, three or four protrusive parts which support the at least one optical element, positions of the two, three or four protrusive parts in a direction of an optical axis being the same, each of the two, three or four protrusive parts being arranged to be substantially in point-contact with the at least one optical element, the two, three or four protrusive parts being disposed in such a way as to enable the light-transmissive surface to be deformed symmetrically with respect to both a first plane which includes the optical axis and a second plane which includes the optical axis and is perpendicular to the first plane.
In accordance with a further aspect of the invention, there is provided a projection aligner, which comprises the lens barrel, the lens barrel having a projecting optical system which includes the optical element, a pattern formed on a mask being projected by the projecting optical system onto a substrate to be exposed.
In accordance with a still further aspect of the invention, there is provided a device manufacturing method for manufacturing a device by using the projection aligner, a mask having a circuit pattern and a substrate to be exposed.
The above and further objects and features of the invention will become apparent from the following detailed description of preferred embodiments thereof taken in conjunction with the accompanying drawings.